1. Field of the Invention
The present invention relates to the field of cellular communications. In particular, the present invention provides a method and apparatus for integrating a cellular zone into a cellular communications network.
2. Description of the Related Art
Currently, cellular networks provide cellular telephone service to wide geographical areas. A cellular network generally comprises a set of overlapping cells, a cell being a geographical area within radio contact of a fixed transmitter, normally known as a base station. Base stations consist of transceivers which send and receive signals to other base stations within a given frequency range as well as to any distributed transceivers (often a cellular phone) with the cell. Cells are positions so as to overlap with each other, thereby providing radio coverage over a greater area than the area of any one cell. Radio communication between base stations is facilitated by placing one base station within the coverage area of another base station. A handing-off protocol enables propagation of a signal from one base station to another and, by extension, throughout the network. Cellular networks are inherently asymmetric with a set of fixed main transceivers each serving a cell and a set of distributed transceivers which provide services to the network's users.
The primary requirement for operation of a cellular network is a way for the distributed transceivers to distinguish between a signal from its own transmitter and a signal from other transmitters. Two common solutions to this are frequency division multiple access (FDMA) and code division multiple access (CDMA). FDMA works by assigning a different operational frequency for each neighbouring cell. By tuning to the frequency of a chosen cell the distributed stations can avoid the signal from other neighbours. CDMA is a form of multiplexing, which enables numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands. CDMA uses spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. In spread spectrum technology, the frequency of the transmitted signal is made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. The CDMA channel is nominally 1.23 MHz wide.
Cellular coverage is typically provided by GSM/CDMA (Global System for Mobile telecommunications/Code Division Multiple Access). GSM is a globally accepted standard for digital cellular communication. In GSM, both signaling and speech channels are digital, which means that it is seen as a second-generation (2G) mobile phone system. GSM systems provide higher digital voice quality and low cost alternatives to making calls, such as text messaging.
New developments are emerging in which a dual mode mobile phone using both 802.11 and GSM/CDMA reside on the same handset. IEEE 802.11, or Wi-Fi, denotes a set of Wireless LAN standards developed by Working Group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802). The term is also used to refer to the original 802.11, which is now sometimes called “802.11 legacy.” The 802.11 family currently includes six over-the-air modulation techniques that all use the same protocol, the most popular (and prolific) techniques are those defined by the a, b, and g amendments to the original standard. 802.11b and 802.11g standards use the unlicensed 2.4 gigahertz (GHz) band. The 802.11a standard uses the 5 GHz band. Operating in an unregulated frequency band, 802.11b and 802.11g equipment can incur interference from microwave ovens, cordless phones, and other appliances using the same 2.4 GHz band. However, using the existing wireless protocols of the cellular carrier enables operating with existing handsets with no modification required.
If the distributed transceivers are mobile and moving from cell to cell, they have to change radio contact from cell to cell. The mechanism for this transfer depends on the type of network and the circumstances of the change. For example, if there is an ongoing continuous communication, then transfer should be made to occur without interruption. In this case, there must be clear coordination between the base station and the mobile station. Typically such systems use some kind of multiple access independently in each cell, so an early stage of such a handover is to reserve a new channel for the mobile station on the new base station which will serve it. The mobile then moves from the channel on its current base station to the new channel and from that point on communication takes place.
With new technologies, there is a need for methods of arbitrating signals between carrier systems. Additionally, as the “wired” and “wireless” worlds of communication come together, and as different types of wireless technologies merge, the issue of carrier signal arbitration and selection becomes increasingly important. New methods will address issues relating to signal platforms. Users typically demand increased signal strength and signal quality. Thus, these new methods should provide improved signal quality.
Although cellular network cover wide areas, there remain geographic areas that are still uncovered, for various reasons. Some of these areas have a small population base (customer base), making it not financially viable to install a cell tower (base station) to provide coverage in those areas. Other areas are too remote to justify installation. In other areas, obstructions such as mountains, hills, trees, etc. degrade performance. In addition, man-made forms of interference, such as power lines, degrade the signal. All of these factors may lead to extremely poor signal quality to no signal in a given area. In the past, commercial organizations have installed special cellular antennas in commercial areas, such as malls, where a cellular user might have a problem accessing a carrier signal through thick concrete and metal. However, there is an ongoing need to provide financially viable cellular coverage in areas that do not have adequate carrier coverage and to arbitrate between signal carriers so as to provide signal coverage.